`ruff --help` previously listed 37 options in no particular order
(with niche options like --isolated being listed before before essential
options such as --select). This commit remedies that and additionally
groups the options by making use of the Clap help_heading feature.
Note that while the source code has previously also referred to
--add-noqa, --show-settings, and --show-files as "subcommands"
this commit intentionally does not list them under the new
Subcommands section since contrary to --explain and --clean
combining them with most of the other options makes sense.